EP2179149B1 - Method and device for diagnosing the operating state of an exhaust line of an internal combustion engine - Google Patents

Description

The present invention relates to the field of the treatment of the exhaust gases of an internal combustion engine, for example a motor vehicle.

The invention relates more particularly to a method and a device for diagnosing the operating state of an exhaust line of such an internal combustion engine.

At the present time, it is sought to minimize the pollutant emissions of internal combustion engines used in motor vehicles, and in particular to reduce or eliminate the emission of soot particles by diesel engines in order to meet anti-diesel standards. -pollution.

For this purpose, it is generally used regeneration means for periodically burning the particles trapped in the particulate filters, so as to avoid clogging of the latter.

These filters are generally associated with diagnostic devices for detecting any malfunctions of the means involved in the removal of particles.

The Applicant has developed diagnostic devices for the operating state of an exhaust line of an internal combustion engine equipped with a particulate filter. In this respect reference may be made to French patent applications FR-A-2,832,758 and FR-A-2,884,862 .

These diagnostic devices comprise means for measuring a differential pressure prevailing between the upstream and the downstream of the particle filter, and a central unit provided with means for detecting stabilized operating points of the engine, means for evaluating a diagnostic parameter from the value of the measured differential pressure and means for processing the parameter of diagnosis evaluated for the detection of a particle filter malfunction, said processing means acting in the event of stabilized operation of the engine.

These devices thus make it possible to overcome the transient phenomena appearing in particular during strong accelerations or decelerations of the motor, which generally generate relatively large measurement noises that can lead to a failure of the diagnostics.

These diagnostic devices are provided for the detection of a plurality of damage levels of the particulate filter in order to know whether it is only necessary to carry out a regeneration, or conversely to provide for its replacement.

However, in the case where it is desired to determine a finer damage level of the particulate filter to know if it is off or not, such devices are insufficient.

The present invention therefore aims to remedy this drawback and to provide a method and a diagnostic device capable of detecting a level of finer damage of a particle filter mounted on the exhaust line of the internal combustion engine and this, economically with increased reliability.

For this purpose, the method for diagnosing the operating state of an exhaust line of an internal combustion engine equipped with a particle filter comprises pressure measuring steps, a step of detecting stable operation, and a step of evaluating a diagnostic parameter from the pressure values measured in case of stable operation of the engine comprising calculating the value of the rolling average of pressure measurements obtained. The document EP-A-1,316,693 describes the features of the preamble of claim 1.

According to one aspect of the invention, the step of detecting stable operating points of the engine comprises feeding the values of engine load and engine speed of operating points considered to a preset map memory of the engine speed according to the engine load, and the determination of stable operating points from this mapping

According to one aspect of this method, the evaluation step of the diagnostic parameter comprises comparing said calculated rolling average value with a predetermined threshold value.

Indeed, the Applicant has determined that the use of the sliding average as a diagnostic parameter of the operating state of the particulate filter makes it particularly easy and effective way to obtain the detection of a malfunction of the filter in order to his replacement.

dans laquelle les points n retenus sont choisis à l'intérieur d'une zone prédéfinie en termes de classes de débit des gaz d'échappement à l'intérieur du filtre.For example, the sliding average is derived from the relation: $$\left({\tilde{P}}_{\mathrm{not}}\right)=\frac{{\tilde{P}}_{\mathrm{not}-\mathit{1}}\mathrm{x}\left(\mathrm{not}-1\right)+P_{\mathrm{not}}}{\mathrm{not}}$$

wherein the selected n-points are selected within a predefined area in terms of exhaust gas flow classes within the filter.

According to an exemplary implementation, at least the pressure upstream of the particulate filter is determined, the value of the diagnostic parameter is continuously calculated for each stable operating point, develops a global diagnostic parameter from the diagnostic parameters of each operating point, and compares the value of the overall diagnostic parameter with a single detection threshold value of a particle filter malfunction so as to determine the state of damage of the particulate filter.

Advantageously, the step of developing overall diagnosis includes a summation of the respective diagnostic parameters of the stable operating points.

In one embodiment, relative pressures are measured upstream of the particulate filter. Alternatively, it is still possible to measure differential pressures across said filter, or to measure absolute pressures upstream of the particulate filter and the atmospheric pressure.

According to the invention, there is also provided a device for diagnosing the operating state of an exhaust line of an internal combustion engine equipped with a particulate filter, the device comprising pressure measuring means. , a central unit provided with means for detecting stable operating points of the engine, and means for evaluating a diagnostic parameter from the measured pressures.

According to a general characteristic, the device further comprises means for calculating the moving average of pressure measurements obtained, a preset memory map of the engine speed as a function of the load of said engine, the detection means being able to determine the points of stable operation of the engine from engine load values and engine speed of operating points considered brought to the map, and means for comparing the calculated rolling average value with a predetermined threshold value.

Advantageously, the device also comprises means for summing the diagnostic parameters for developing an overall diagnostic parameter and means for comparing said global diagnostic parameter with a particle filter malfunction detection threshold value.

Preferably, the measuring means comprise a pressure sensor mounted immediately upstream of the particulate filter.

The diagnostic device can advantageously be used in a diesel engine.

• la figure 1 est une vue schématique d'un moteur à combustion interne équipé d'une ligne d'échappement pourvue d'un filtre à particules associé à un dispositif de diagnostic selon l'invention ;
• la figure 2 représente l'évolution de la contre-pression à l'échappement de filtres à particules en fonction du débit volumique des gaz d'échappement, et
• la figure 3 illustre schématiquement les différentes étapes de fonctionnement du dispositif de diagnostic de la figure 1 ;

The invention will be better understood from the study of a particular embodiment, taken by way of non-limiting example and illustrated by the appended drawings, in which:

• the figure 1 is a schematic view of an internal combustion engine equipped with an exhaust line provided with a particulate filter associated with a diagnostic device according to the invention;
• the figure 2 represents the evolution of the exhaust back-pressure of particulate filters as a function of the volume flow rate of the exhaust gases, and
• the figure 3 schematically illustrates the different steps of operation of the diagnostic device of the figure 1 ;

On the figure 1 schematically shows the general structure of an internal combustion engine, designated by the general reference numeral 1.

In the embodiment under consideration, the engine 1 is provided with four cylinders 2 in line. Of course, it is also conceivable to provide a motor 1 having a different number of cylinders 2. The cylinders 2 are supplied with air via an intake distributor 3, which is fed by a pipe 4 provided with an air filter (not shown), and a turbocharger 5 supercharging air. The turbocharger 5 is connected to the intake distributor 3 via a pipe 6.

The cylinders 2 are also connected to an exhaust manifold 7 recovering the exhaust gases from the combustion and discharging the latter through a pipe 8 to the compressor 5, said gases then being discharged to the outside by an exhaust line 9 connected to the compressor 5.

The exhaust line 9 comprises a particulate filter 10 adapted to trap the particles or soot contained in the exhaust gas. In a manner known per se, the particulate filter 10 comprises means, for example electrostatic, for trapping these particles or soot.

Of course, it is also conceivable to further provide an oxidation catalyst or an NO _x trap (x = 1 or x = 2) mounted on the exhaust line 9 upstream of the particulate filter 10, considering the flow direction of the exhaust gas.

The engine 1 is associated with a central unit 12 ensuring the operational control of said engine, including the adjustment of its operating parameters, as well as the operating control of the particulate filter 10, and the diagnosis of its operating state.

To carry out the control of the operation of the engine, it is essentially provided with a flow sensor 13 mounted on the supply line 4, upstream of the turbocharger 5. The flow sensor 13 is connected to the central unit 12 , via a referenced connection 14 schematically illustrated in dotted lines.

With regard to the control of the operation of the particulate filter 10 or, in general, of the exhaust line 9, and in particular the diagnosis of its operating state, this is provided with a sensor of pressure and temperature 15 capable of measuring the relative pressure and the temperature upstream of the particulate filter 10. The pressure sensor 15 is mounted here immediately upstream of the particulate filter 10.

The sensor 15 is connected to the central unit 12 via a connection 16. The central unit 12 also receives, via a connection 17, information relating to the operation of the motor, for example the engine speed N _word and engine load Ch _word .

The central processing unit 12 includes, stored in memory, all the material and logistical means for controlling the operation of the particle filter 10, in particular from the relative pressure upstream of the particle filter 10 detected by the sensor 15. , by calculating, from this pressure value, the value of a diagnostic parameter and treating the value of this parameter to detect any malfunction that may occur, as will be described.

The main steps of the diagnostic method implemented in the central unit 16 will now be described. The method according to the invention is based on the principle of diagnosing the level of damage of the particulate filter. The figure 2 presents the plot of the exhaust back-pressure of particulate filters as a function of the volume flow rate of the exhaust gases in the exhaust line. This figure shows the plot of this pressure for an integrated particle filter, and first and second damaged filters. The volume flow-pressure ratio makes it possible to differentiate an integrated particulate filter from a damaged particulate filter. The diagnostic method according to the present invention aims to reliably diagnose damage to a filter such as that illustrated for the first damaged filter illustrated in this figure.

dans laquelle :

• K désigne une constante,
• Q_air représente le débit d'air massique mesuré par le débitmètre 13 (figure 1),
• ρ_fuel désigne la densité du gazole injectée,
• Q_carb désigne la quantité de gazole injectée,
• N représente le régime du moteur,
• T_amont représente la température en amont du filtre à particules, et
• P_amont représente la pression absolue en amont du filtre à particules.

Referring now to the figure 3 , in order to detect the stabilized operating points, one calculates, in a first step, during step 20, the value of volume flow rate Q _vol of the exhaust gas in the particulate filter. To do this, we use the relation: $${\mathrm{Q}}_{\mathrm{flight}}=\mathrm{K}\times \left({\mathrm{Q}}_{\mathrm{air}}+{\mathrm{\rho }}_{\mathrm{fuel\; oil}}\times {\mathrm{Q}}_{\mathrm{carb}}\right)\times \mathrm{NOT}\times \left(\frac{{\mathit{T}}_{\mathit{uphill}}}{{\mathit{P}}_{\mathit{uphill}}}\right)$$

in which :

• K denotes a constant,
• Q _air represents the mass air flow rate measured by the flowmeter 13 ( figure 1 )
• ρ _fuel is the density of the diesel fuel injected,
• Q _carb means the quantity of diesel fuel injected,
• N represents the engine speed,
• T _upstream represents the temperature upstream of the particulate filter, and
• P _upstream represents the absolute pressure upstream of the particulate filter.

At the same time, during this step 20, the value P of the relative pressure upstream of the particulate filter measured by the sensor 15 is acquired.

Then, at the next step 21, the value P of the pressure and the Q value of the calculated _flight volume flow filtered. In storage means, during step 22, a pair (Q _vol , P) of a determined volume flow rate of the exhaust and pressure gases corresponding to the operating point retained is stored. Each pair (Q _vol , P) is indexed according to predetermined classes of volume flow inside the particle filter 10, for example 100-199 m ³ / h, 200-299 etc.

In parallel with steps 20 to 22, during a step 23, it is verified that the operating point retained corresponds to a stabilized operating point of the motor. In this respect, we bring engine _word Ch information and engine speed N _word to a previously established memory map. On the memorized map of the engine speed N _word according to the engine load Ch _word , it is established, by prior learning, a range of engine operation in which operating points are considered to be in a transient state. From the stored map, it is then determined whether the operating point considered is a stabilized operating point of the motor or not.

In the case where it is detected that the operating point in question is a stabilized operating point for the motor, so as to overcome the measuring noises resulting from the transient phases, the process then continues with a diagnostic phase of the operating state of the particulate filter.

$${\bar{P}}_0={\mathrm{P}}_0$$

dans laquelle P _n représente la valeur moyenne glissante de mesures de la pression obtenue par le capteur 15, pour un point n considéré.This phase begins with a first step 24, during which the diagnostic parameter of the operating state of the particulate filter is developed. This diagnostic parameter is developed from the following relation: $$\left({\tilde{P}}_{\mathrm{not}}\right)=\frac{{\tilde{P}}_{\mathrm{not}-1}\mathrm{x}\left(\mathrm{not}-1\right)+{\mathrm{P}}_{\mathrm{not}}}{\mathrm{not}}$$

$${\tilde{P}}_0={\mathrm{P}}_0$$

in which P _n represents the sliding average value of measurements of the pressure obtained by the sensor 15, for a point n considered.

A pre-defined number n of points is taken into account, these points being chosen within the same predetermined class of volume flow inside the particle filter 10.

In the next step 25, the value of the diagnostic parameter is compared P _n thus calculated with a predetermined threshold value SI. In the case where the diagnostic parameter is less than the threshold value S1, a binary value b1 is set at 1 for the operating point i considered, during step 26.

Then, during the next step 27, a global diagnostic parameter is developed for all the stable operating points. To do this, the sum of the binary values obtained in step 26 is carried out.

A test is then performed by comparing the value of global diagnostic parameters with a single particle filter malfunction detection threshold, during step 28.

Thus, if it is detected, during this step 28, that the overall diagnostic parameter is greater than the threshold value, it is decided that the particulate filter is damaged and that it should be replaced.

Thanks to the invention, there is thus a method for determining whether the particulate filter has retained its integrity or, conversely, whether it must be replaced, in particular by calculating an average of the backpressure at the same time. exhaust generated on the filter on a predefined class of volume flow through said filter.

Although in the embodiment previously described, a relative pressure is detected upstream of the particle filter to diagnose the state of damage thereof, it is also conceivable that it is also possible, without leaving of the present invention, detecting the damage via a differential pressure sensor, or an absolute pressure sensor upstream of the particulate filter.

Claims (11)

1. Method for diagnosing the operating state of an exhaust line of an internal combustion engine which line is equipped with a particle filter, comprising steps of measuring pressure, a step of detecting stable engine operating points, and a step of evaluating a diagnostics parameter from the pressure values measured if the engine is operating stably, involving calculating the value of the sliding mean ( P _n) of pressure measurements obtained, characterized in that the step of detecting stable engine operating points involves bringing the engine load (Ch_mot) and engine speed (N_mot) values of operating points considered to a pre-established map stored in memory of engine speed as a function of engine load and determining stable operating points from this map, and in that the step of evaluating the diagnostics parameter involves comparing the said calculated sliding mean value against a predetermined threshold value (S1).
2. Method according to Claim 1, in which the sliding mean ( P _n) is formulated from the relationship: $$\left({\bar{P}}_n\right)=\frac{{\bar{P}}_{n-\mathit{1}}\mathrm{x}\left(\mathrm{n}-1\right)+P_n}{\mathrm{n}}$$

   

   in which the points n adopted are chosen to lie inside a predefined zone in terms of classes of flow rate of exhaust gases inside the filter.
3. Method according to either one of the preceding claims, in which at least the pressure upstream of the particle filter is determined, the value of the diagnostics parameter is calculated continuously for each stable operating point, an overall diagnostics parameter is formulated from the diagnostics parameters for each operating point, and the value of the overall diagnostics parameter is compared against a single threshold value for the detection of a malfunction of the particle filter so as to determine the state of damage of the particle filter.
4. Method according to Claim 3, characterized in that the step of formulating the overall diagnosis involves summing the respective diagnostics parameters for the stable operating points.
5. Method according to any one of the preceding claims, in which gauge pressures upstream of the particle filter are measured.
6. Method according to any one of Claims 1 to 4, in which differential pressures across the particle filter are measured.
7. Method according to any one of Claims 1 to 4, in which absolute pressures upstream of the particle filter and atmospheric pressure are measured.
8. Device for diagnosing the state of operation of an exhaust line of an internal combustion engine which line is equipped with a particle filter (10), comprising pressure measuring means (15), a central unit (12) provided with means of detecting stable engine operating points, with means of evaluating a diagnostics parameter from the pressures measured, and with means of calculating the sliding mean ( P _n ) of pressure measurements obtained, characterized in that it further comprises a pre-established map of engine speed as a function of engine load stored in memory, the detection means being able to determine the stable engine operating points from engine load (Ch_mot) and engine speed (N_mot) values of operating points considered referred to the map, and from means of comparing the said calculated value of the sliding mean against a predetermined threshold value (S1).
9. Device according to Claim 8, comprising means of summing the diagnostics parameters in order to formulate an overall diagnostics parameter and means of comparing the said overall diagnostics parameter against a threshold value for detecting the malfunctioning of the particle filter.
10. Device according to Claim 8 or 9, in which the measurement means (15) comprise a pressure sensor mounted immediately upstream of the particle filter (18).
11. Use of a diagnostics device according to any one of Claims 8 to 10 in a diesel engine.

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